In the production of colored fabrics, it is highly desirable to test the color of the fabrics to be sure that the dyeing operation is working satisfactorily, and to ensure that the color of the fabric is appropriate for the end use desired.
Perhaps the most common commercial practice for measuring the color of rolls of fabric comprises cutting a six-inch full-width swatch from the end of each roll, and measuring the swatch in one or two spots and averaging the readings to obtain a representative color value for the roll. Most color instrumentation that is used for this purpose is capable of viewing only a relatively small area (e.g. about 1-3 square inches). While this approach is acceptable for solid shade fabrics, for fabrics having inherent color variations within relatively small areas, such as denim, plaids, checks, patterned, and multi-color fabrics (i.e. non-solid-shade fabrics) it is not. In commercial practice non-solid-shade fabrics cannot be reliably measured without extensive reading and averaging of results taken from many different locations on the swatch, a time consuming and commercially impractical approach.
Other commercially available color monitoring equipment is designed to sample a "roll" of fabric without the necessity of cutting swatches by traversing laterally at the same time that the cloth moves longitudinally beneath it, taking a reading each time it encounters the left side, center, and right side of the fabric, taking readings at speeds of up to seven readings per second. Such equipment cannot provide detailed analysis of shade changes across the width of the fabric, and thus the apparatus is limited, for practical use, to solid shade fabrics.
According to the present invention, it is possible for the first time to accurately determine color properties, such as average color and/or excursions outside predetermined acceptable color limits, of non-solid-shade fabrics. Typical non-solid-shade fabrics on which the invention may be utilized include denim, patterned fabrics (e.g. checks and plaids), crushed velours, pile fabrics, and fabrics containing fancy (slub) yarns. This is accomplished according to the invention by continuously sampling a fabric swatch, typically having a six-inch width and a 60-inch length (corresponding to the 60-inch width of a fabric roll). Typically about 400-1,000 readings would be taken along the length of the swatch. These readings can be taken in a fast and effective manner according to the invention by continuously moving the swatch with respect to a colorimeter head, continuously sampling the swatch with the colorimeter head at a rate of at least about 100 readings per second, continuously passing the analog signals from the colorimeter directly to an analog-to-digital (A/D) convertor, continuously converting the analog signals from the colorimeter to digital signals utilizing the A/D convertor and passing the digital signals to storage in a computer (e.g. microprocessor), and after completion of the continuous sampling, analyzing the stored digital signals with the computer to determine average color and/or excursions outside acceptable limits of color. The invention is particularly effective when mechanical apparatus is associated with the colorimeter for continuously moving the fabric swatch with respect to the colorimeter, although movement can be effected by hand.
An advantage of the invention is that the color reading aspects thereof can be readily performed with conventionally available equipment. The colorimeter head itself is a conventional four filter colorimeter head having red, green, and blue filters operatively associated with conventional photo-detectors and in operative association with an electrically powered light source. The colorimeter preferably is of the type manufactured by Hunter Associates Laboratory, Inc., of Reston, Va. However only the head (including the filters, photo-detectors, and light source) of a Hunter colorimeter is utilized, not conventional A/D convertors, microprocessors, or cablings that are associated with it. Rather, according to the invention, an A/D convertor board manufactured by Data Translation Company is utilized, and it is connected up to a DEC microprocessor, such as a Model PDP 11/73. This provides sufficient capacity to continuously receive and store all of the readings from across the entire length of the fabric swatch (e.g. about 400-1,000 readings), and then to perform appropriate analysis after reading is completed.
According to the present invention it is also desirable to monitor the voltage to the light source of the colorimeter head to calibrate the analog signals, and ultimately the digital signals from the A/D convertor, depending upon the voltage to the light source. This can be effected utilizing a simple voltage divider operativey connected to the power lines to the light source, and to a DB 25-5 connector, or the like, which is operatively connected to the colorimeter head, photo-detectors and ultimately to the A/D board.
The invention also contemplates apparatus for moving a swatch of fabric with respect to the colorimeter. Typically the colorimeter head has a housing with a generally planar surface having a viewing port therein and over which the fabric swatch, in non-rigid form (i.e. unbacked) is passed. Swatch detection means, such as a pair of optical detectors, are mounted on the generally planar surface at a first .idse of the viewing port and swatch moving means are mounted on the generally planar surface and extend from the swatch detection means toward and to a second side of the viewing port, opposite the first side, for engaging a swatch of fabric resting on the housing generally planar surface and moving the fabric from the first side of the viewing port to the second side thereof. The swatch moving means includes power means. The swatch moving means preferably comprises first and second rollers that are connected by a belt with one of the rollers driven through a drive mechanism by an electric motor. Adjustment means are provided for adjusting the swatch moving means with respect to the housing surface to accommodate fabric swatches of different dimensions.
In order to allow the sample swatch to be moved across the viewing port in any direction while maintaining an optically acceptable viewing surface it is desirable to provide a positive pressure system such as shown in U.S. Pat. No. 4,346,997 (the disclosure of which is hereby incorporated by reference herein) for the colorimeter head. In such a system, fluid is continuously supplied under pressure to the colorimeter head to exhaust through the viewing port to prevent sample lint and dust from entering the head, to facilitate removal of heat that has been generated by the colorimeter, and to facilitate maintenance of a sample so that a flat, distortion-free surface can be examined; and exhausting the fluid supplied to the head from a location distinct from the viewing port when the viewing port is covered with a sample swatch to be examined.
It is the primary object of the present invention to provide for the effective and accurate determination of average color and/or excursion outside predetermined acceptable color limits for fabrics, including non-solid-shade fabrics. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.